Diafiltration is a technique that uses ultrafiltration (UF) membranes to remove, replace, or lower the concentration of undesirable materials such as salts and/or solvents from fluids containing desirable materials, for example, desired biomolecules such as proteins, peptides, and nucleic acids. A UF membrane retains molecules that are larger than the pores of the membrane (the solution containing the retained molecules is referred to as the retentate or concentrate), and smaller molecules such as salts, solvents, and water (which are 100% permeable), freely pass through the membrane (providing a solution referred to as the permeate or filtrate).
Continuous diafiltration (sometimes referred to as constant volume diafiltration) involves washing out the original buffer salts (and/or other low molecular weight species) in the retentate by adding water or new buffer to the retentate at the same rate as filtrate is being generated. As a result, the retentate volume and product concentration does not change during the diafiltration process. If water is used for diafiltering, the salts will be washed out and the conductivity lowered. If a buffer is used for diafiltering, the new buffer salt concentration will increase at a rate inversely proportional to that of the species being removed, and the conductivity will be increased. The amount of salt removed is related to the filtrate volume generated, relative to the retentate volume. The filtrate volume generated is usually referred to in terms of “diafiltration volumes.” A single diafiltration volume (DV) is the volume of retentate when diafiltration is started. For continuous diafiltration, liquid is added at the same rate as filtrate is generated. When the volume of filtrate collected equals the starting retentate volume, 1 DV has been processed. Using continuous diafiltration, greater than 99.5% of a 100% permeable solute can be removed by washing through 6 retentate volumes (6 DV) with the buffer of choice.
However, there is a need for improved diafiltration systems and methods.
The present invention provides for ameliorating at least some of the disadvantages of the prior art. These and other advantages of the present invention will be apparent from the description as set forth below.